Hereinafter, a conventional chip-shaped electronic part is described referring to the drawings.
FIG. 11 is a cross-sectional view of a chip resistor, as an example of the conventional chip-shaped electronic part. A substrate 1 is made of ceramics such as alumina, and has an insulation property. The thickness of the substrate 1 is decreased, as the size of the chip-shaped electronic part is decreased. For instance, a substrate 1 of a 0603 chip resistor with the outer dimensions of 0.6 mm×0.3 mm has a standard thickness of 0.2 mm, and a substrate 1 of a 0402 chip resistor with the outer dimensions of 0.4 mm×0.2 mm has a standard thickness of 0.1 mm.
A pair of upper surface electrodes 2 are formed at widthwise both ends on an upper surface of the substrate 1. The upper surface electrode pair 2 generally has a film thickness of about 8 μm. A resistive element 3 is formed on the upper surface of the substrate 1 so that both ends thereof are placed over the upper surface electrode pair 2. The resistive element 3 generally has a thickness of about 8 μm. A pre-coat glass layer 4 is formed in such a manner as to cover the resistive element 3. The pre-coat glass layer 4 generally has a thickness of about 8 μm. A protective film 6 is formed in such a manner as to cover the entirety of the resistive element 3. The protective film 6 has a thickness from 10 μm to 30 μm at a portion above the resistive element 3. Accordingly, the protective film 6 has an upwardly convex shape in cross section with respect to a middle portion thereof including its vicinity resulting from a surface tension.
A pair of lower surface electrodes 5 are formed on a lower surface of the substrate 1 at positions opposing the upper surface electrode pair 2. A pair of end surface electrodes 7 are formed on end surfaces of the substrate 1 in such a manner as to be electrically connected to the upper surface electrode pair 2 and to the lower surface electrode pair 5. A nickel plated layer 8 is formed on parts of surfaces of the upper surface electrode pair 2, surfaces of the end surface electrode pair 7, and surfaces of the lower surface electrode pair 5. A solder plated layer 9 is formed in such a manner as to cover the nickel plated layer 8. The solder plated layer 9 is formed at a position lower than the middle portion of the protective film 6.
Next, a process for manufacturing the chip resistor as an example of the conventional chip-shaped electronic part is described referring to the drawings.
FIGS. 12A through 12C, and 13A through 13C are manufacturing process diagrams on the conventional chip resistor. The manufacturing method is described referring to FIGS. 12A through 12C, and 13A through 13C.
First as shown in FIG. 12A, prepared is a sheet-like substrate 1c made of ceramics such as alumina and having an insulation property, in which first dividing grooves 1a and second dividing grooves 1b are formed in each of the upper surface and the lower surface of the sheet-like substrate 1c. A number of upper surface electrodes 2 are formed on the upper surface of the sheet-like substrate 1c by a screen printing method in such a manner as to bridge over the first dividing grooves 1a. Although not illustrated, a number of lower surface electrodes 5 are formed on the lower surface of the sheet-like substrate 1c in such a manner as to bridge over the first dividing grooves 1a. 
Next, as shown in FIG. 12B, resistive elements 3 are formed on the upper surface of the sheet-like substrate 1c by a screen printing method in such a manner as to be partially placed over the upper surface electrodes 2. Then, pre-coat glass layers 4 are formed by a screen printing method in such a manner as to cover the resistive elements 3. Then, trimming grooves 3a are formed in the resistive elements 3 through the pre-coat glass layers 4 by a laser or a like device so that a total resistance of the resistive elements 3 lies within a predetermined resistance range.
Next, as shown in FIG. 12C, protective films 6 are formed by a screen printing method in such a manner as to cover the resistive elements 3.
Next, a strip-shaped substrate 1d as shown in FIG. 13A is formed by dividing the sheet-like substrate 1c along the first dividing grooves 1a shown in FIG. 12C. Then, end surface electrodes 7 are formed by coating on end surfaces of the strip-shaped substrate 1d so that the end surface electrodes 7 are electrically connected to the upper surface electrodes 2 and to the lower surface electrodes 54.
Next, pieces of substrate 1e as shown in FIG. 13B are formed by dividing the strip-shaped substrate 1d shown in FIG. 13A along the second dividing grooves 1b. 
Lastly, as shown in FIG. 13C, a nickel plated layer 8 (not shown) is formed on parts of the surfaces of the upper surface electrodes 2, the surfaces of the lower surface electrodes 5, and the surfaces of the end surface electrodes 7, followed by forming a solder plated layer 9. Thus, the conventional chip resistor is produced.
As an example of the prior art document information pertaining to the invention of the application, there is known Japanese Unexamined Patent Publication No. Hei 7-86003 (patent document 1).
The conventional chip resistor is mounted on a printed circuit board of an electronic device by soldering the lower surface electrodes 5 of the chip resistor to electrode lands 10b of the printed circuit board 10a, as shown in FIG. 14. In the mounting, the lower surface electrodes 5 of the chip resistor are positioned to the electrode lands 10b of the printed circuit board 10a, with the upper surface of the protective film 6 being attached to a mounting nozzle 10c by suction. In this arrangement, a pressing force is intensively exerted on the middle portion of the protective film 6 including its vicinity, which corresponds to a protrusion on the upper surface of the chip resistor, and a large force to bend the substrate 1 is acted in combination with a repulsive force received on the lower surface electrode pair 5, which corresponds to protrusions on the lower surface of the chip resistor. Thereby, a large bending stress is exerted on the substrate 1. As a result, as shown in FIG. 15, the substrate 1 may be cracked. In particular, the substrate crack is serious, if the substrate 1 with a small thickness is used in the small-sized chip-shaped electronic part e.g. a 0603 chip resistor with the outer dimensions of 0.6 mm×0.3 mm, or a 0402 chip resistor with the outer dimensions of 0.4 mm×0.2 mm.